1. Viral and Bacterial Genetics Chapter 18

2. Overview Comparison Figure 18.2 0.25  m

3. Overview Comparison Eukaryotes Plant, Animal, Fungi or “Protist” Cells Nucleus – DNA – Iinear chromosomes w/ histone proteins Cell Membrane (and cell wall in plants and fungi) – Cellulose or chitin cell wall Large Ribosomes Energy (ATP) in Mitochondria Complex Viruses Not cells No Nucleus or nucleoid – DNA or RNA Protein Coat – Capsid No Ribosomes No Energy – Host cell Simplest Archaea or Bacteria Cells No Nucleus – nucleiod region –DNA – circular w/o histone proteins Cell Membrane and Cell Wall – Peptidoglycan cell wall - bacteria Small Ribsomes Energy (ATP) in Cell Membrane Simple Prokaryotes

4. Viral Structure Infectious (parasitic) particles with nucleic acids enclosed in a protein coat - capsid Nucleic Acids – DNA or RNA – Double stranded DNA – Single stranded DNA – Double stranded RNA – Single stranded RNA

5. Viral Structure Capsid – protein coat covering - capsomeres – Rod shaped – Polyhedral – complex Envelope – surrounds the capsid of some viruses – Host cell phospholipids and proteins – Glycoprotein spikes Tail – found on bacteriophages – Viruses that infect bacteria as the host

7. Viral Structure Draw a virus and label the parts Describe the features all viruses share.

8. Host Cell Each type of virus can only infect a certain range of host cells – host range Use “lock and key” fit between host cell receptors and virus Host cell provides the “machinery” to reproduce the viral genome – tRNA – Ribosomes – amino acids – Polymerases – ATP Virus hijacks the host cell – parasite

9. VIRUS Capsid proteins mRNA Viral DNA HOST CELL Viral DNA DNA Capsid Figure 18.5

10. Viral - Bacteriophage Reproduction Lytic Cycle – Virus kills the host cell – Uses it to reproduce then lyses (blows up) the cell releasing new viruses to infect new host cells – Virulent phages (bacteriophages) Lysogenic Cycle – Virus reproduces its genome without destroying the host cell – “Dormant cycle” – Can switch to lytic cycle at any time

11. Phage assembly Head Tails Tail fibers Figure 18.6

12. Many cell divisions produce a large population of bacteria infected with the prophage. The bacterium reproduces normally, copying the prophage and transmitting it to daughter cells. Phage DNA integrates into the bacterial chromosome, becoming a prophage. New phage DNA and proteins are synthesized and assembled into phages. Occasionally, a prophage exits the bacterial chromosome, initiating a lytic cycle. Certain factors determine whether The phage attaches to a host cell and injects its DNA. Phage DNA circularizes The cell lyses, releasing phages. Lytic cycle is induced Lysogenic cycle is entered Lysogenic cycleLytic cycle or Prophage Bacterial chromosome Phage DNA Figure 18.7

13. IQ 18.1 Describe the “life” cycle of a virus Include Lytic and lysogenic phases

14. Aminal Enveloped Viruses Glycoproteins fuse with receptors on host cell membrane Capsid enters host cell Viral genome replicates New virus leaves the host cell through the cell membrane RNA Capsid Envelope (with glycoproteins) HOST CELL Viral genome (RNA) Template Capsid proteins Glyco- proteins mRNA Copy of genome (RNA) ER Figure 18.8

15. Retroviruses RNA virus that uses reverse transcriptase to create DNA DNA is then incorporated into the cells chromosome and transcribed and translated with the rest of the cells genes. Provirus – becomes a permanent part of the cells DNA – HIV Figure 18.9 Reverse transcriptase Viral envelope Capsid Glycoprotein RNA (two identical strands)

16. Figure 18.10 mRNA RNA genome for the next viral generation Viral RNA RNA-DNA hybrid DNA Chromosomal DNA NUCLEUS Provirus HOST CELL Reverse transcriptase New HIV leaving a cell HIV entering a cell 0.25 µm HIV Membrane of white blood cell The virus fuses with the cell’s plasma membrane. The capsid proteins are removed, releasing the viral proteins and RNA. 1 Reverse transcriptase catalyzes the synthesis of a DNA strand complementary to the viral RNA. 2 Reverse transcriptase catalyzes the synthesis of a second DNA strand complementary to the first. 3 The double-stranded DNA is incorporated as a provirus into the cell’s DNA. 4 Proviral genes are transcribed into RNA molecules, which serve as genomes for the next viral generation and as mRNAs for translation into viral proteins. 5 The viral proteins include capsid proteins and reverse transcriptase (made in the cytosol) and envelope glycoproteins (made in the ER). 6 Vesicles transport the glycoproteins from the ER to the cell’s plasma membrane. 7 Capsids are assembled around viral genomes and reverse transcriptase molecules. 8 New viruses bud off from the host cell. 9

17. Viral Treatments None – Antibiotics only work against bacteria Prevention – vaccines – Weak or “dead” viruses that trigger an immune response so the body can fight the real thing.

18. IQ 18.2 Explain how the HIV virus works.

19. Bacterial Structure Prokaryotes No Nucleus – nucleoid – Circular bacterial chromosome w/o histone proteins – Plasmid – 2 nd circular chromosome in some bacteria No membrane bound organelles Replication is via binary fission – Fast – double every 15 minutes Replication fork Origin of replication Termination of replication

20. Genetic Recombination The production of new strains of bacteria – creates genetic diversity Transformation Transduction Conjugation Transposable Elements

21. Transformation Uptake of new foreign DNA from the surrounding environment into the bacteria cells genome Produces recombinant DNA – DNA from two different sources – Used in genetic engineering

22. Transduction Involves bacteriophages and 2 host cells Transfer bacterial genes from one host cell to another

23. Conjugation Bacterial “sex” Two bacteria transfer genetic information via a sex pilus F plasmid produces the pili R plasmids create antibiotic resistance

24. Transposable Elements “Jumping genes” Genes that can move from one location to another on the bacterial chromosome – Genetic shuffling – Mutate and become drug resistant antibiotic resistance

25. Bubble Map Bacterial Genetic Recombination

26. Summary